Parallel calls to Repository.ObjectDatabase.CreateBlob with identical contents fails.

I would like to insert blobs from memory into an object database in parallel (based on the technique described at http://stackoverflow.com/a/16244234). This works fine most of the time, but is subject to race conditions if the contents are the same. There are two classes of errors I observe:
1. Exception due to FILE_EXISTS conflict when trying to create the directory with the first two characters of the OID under objects.
2. NULL blob returned from CreateBlob.

Here's some example code to reproduce the problem:

using System;
using System.Text;
using System.IO;
using System.Threading.Tasks;
using LibGit2Sharp;

namespace GitODBStress
{
    class Program
    {
        static void Main()
        {

            string repoPath = Path.Combine(Path.GetTempPath(), "Git_Parallel_Odb");
            int iterationCount = 100;

            if (!Directory.Exists(repoPath))
            {
                Directory.CreateDirectory(repoPath);
            }

            var path = Repository.Init(repoPath, isBare:true);
            Console.WriteLine("Made repo at {0}", path);

            var repo = new Repository(path);

            var tasks = new Task[2];
            for (int i = 0; i < iterationCount; ++i)
            {
                var iter = i;
                byte[] buf = Encoding.ASCII.GetBytes("foo" + iter.ToString());
                for (int taskNo = 0; taskNo < 2; ++taskNo)
                {
                    tasks[taskNo] = Task.Factory.StartNew(() =>
                        {
                            MemoryStream ms = new MemoryStream(buf);
                            for (; ; )
                            {
                                try
                                {
                                    var blob = repo.ObjectDatabase.CreateBlob(ms);
                                    if (blob == null)
                                    {
                                        Console.WriteLine("ERROR: NULL blob on iteration {0}", iter);
                                        continue;
                                    }

                                    break;
                                }
                                catch (LibGit2SharpException e)
                                {
                                    Console.WriteLine("ERROR: Caught LibGit2SharpException on iteration {0}: {1}", iter, e.Message);
                                    if (e.Message.Contains("Cannot create a file when that file already exists."))
                                    {
                                        continue;
                                    }
                                }
                            }
                        });
                }

                Task.WaitAll(tasks);
            }

            repo.Dispose();

            // clean up temp repo files
            var files = Directory.GetFiles(repoPath, "*.*", SearchOption.AllDirectories);
            foreach (var f in files)
            {
                var attrib = File.GetAttributes(f);
                if (attrib.HasFlag(FileAttributes.ReadOnly))
                {
                    File.SetAttributes(f, attrib & ~FileAttributes.ReadOnly);
                }
            }

            Directory.Delete(repoPath, true);
        }
    }
}

Thanks!

Inizia da Repository.ObjectDatabase.CreateBlob ed esegui la riproduzione in C# su un repository bare. Traccia il percorso parallelo per contenuti identici e gli esiti FILE_EXISTS e null-blob segnalati. Il lavoro è completato quando le chiamate concorrenti terminano senza nessuno dei due errori creando il blob previsto.